We propose an approach to generating 6- channel polarity-inverted ultra-wideband (UWB) doublets by utilizing the parallel fiber-optical parametric amplifier (FOPA) configuration. The pulse-splitting effect in a highly nonlinear fiber (HNLF) is exploited to generate the double-overshoot and the double-undershoot, which are the basic components required to form a UWB pulse. Under the circumstances of different relative time advance/delays (RTADs) and different initial Gaussian pulse durations, the key parameters, including center frequency (Fc), 10-dB bandwidth (BW10dB) and fractional bandwidth (FBW) for a UWB doublet are systematically investigated, eventually proved in line with the U. S. Federal Communications Commission (FCC) regulation.